Apparatus having refrigeration cycle

ABSTRACT

In an apparatus having a refrigeration cycle, the refrigeration cycle is formed by annularly connecting a compressor, a condenser, an expansion device and an evaporator with one another, the apparatus uses propane, isobutane or ethane as a refrigerant, and uses refrigerating machine oil having less mutual solubility with the refrigerant, and a dryer is provided in the refrigeration cycle for absorbing water. In stead of the dryer, an additive which reacts with water may be included in said refrigerating machine oil. With this arrangement, the amount of the refrigerant can be reduced, and the long term reliability of the apparatus can be obtained.

This application is a divisional of Ser. No. 09/258,343, filed Feb. 26,1999, now U.S. Pat. No. 6,044,660.

TECHNICAL FIELD

The present invention relates to an apparatus having a refrigerationcycle, which uses a flammable refrigerant comprising, as a maincomponent, one of propane (R290), isobutane (R600a) and ethane (R170),or a mixture of a plurality of these components.

BACKGROUND TECHNIQUE

At present, Freon-based refrigerants that have stable properties and areeasy to be handled are used as refrigerants of an apparatus having arefrigeration cycle such as a refrigerator and an air conditioner.

However, although the Freon refrigerants have stable properties and areeasy to be handled, it is said that the Freon refrigerants destroy theozone layer, and since the Freon refrigerants adversely affect theglobal environment, the use of the Freon refrigerants will be entirelyprohibited in the future after a preparatory period of time. Among theFreon refrigerants, hydro fluorocarbon (HFC) refrigerants do not seem todestroy the ozone layer, but they have properties to facilitate theglobal warming. Especially in Europe where the people are concernedabout environmental problems, there is a tendency to prohibit the use ofthis refrigerant also. That is, there is a tendency that the use of theFreon refrigerants that are artificially produced is prohibited, andnatural refrigerants such as hydrocarbon are used as in the past.However, such natural refrigerants are flammable, and limited resourcesmust be used effectively, there is a problem that the amount of usagemust be controlled.

Therefore, when refrigerant such as propane or isobutane is used in theapparatus having the refrigeration cycle, in order to reduce the amountof refrigerant to be used, it is effective to use refrigerating machineoil having less mutual solubility with the refrigerant.

However, in order to reduce the mutual solubility between therefrigerant and the refrigerating machine oil, since the polarity of therefrigerant is almost nonpolar, it is effective to use refrigeratingmachine oil having great polarity, but there is a problem thatrefrigerating machine oil having great polarity is liable to absorbwater, and refrigerating machine oil which absorbs water is decomposedby strong sliding movement.

Thereupon, it is an object of the present invention to prevent thedecomposition of refrigerating machine oil due to absorption of water,and to reduce the amount of refrigerant used in an apparatus having arefrigeration cycle by using refrigerating machine oil having lessmutual solubility with the refrigerant.

Another object of the invention is to further reduce the amount ofrefrigerant used in the apparatus having the refrigeration cycle byusing refrigerating machine oil suitable for reducing the refrigerant.

Another object of the invention is to provide an apparatus having arefrigeration cycle capable of obtaining the long term reliability byusing refrigerating machine oil which generates few sediment and whichis excellent in sealing performance and lubricating performance ofsliding surface.

DISCLOSURE OF THE INVENTION

In a refrigeration cycle formed by annularly connecting a compressor, acondenser, an expansion device and an evaporator with one another, thepresent invention relates to an apparatus having such a refrigerationcycle, which uses a refrigerant comprising, as a main component, one ofpropane, isobutane and ethane, or a mixture of a plurality of thesecomponents, and uses refrigerating machine oil for the compressor havingless mutual solubility with the refrigerant.

Therefore, according to the present invention, it is possible to reducethe solution amount of refrigerant into the refrigerating machine oil byselecting such refrigerant and refrigerating machine oil, and to reducethe amount of refrigerant to be charged into the apparatus having therefrigeration cycle.

To achieve the above object, according to a first aspect of the presentinvention, there is provided an apparatus having a refrigeration cycle,where the refrigeration cycle is formed by annularly connecting acompressor, a condenser, an expansion device and an evaporator with oneanother, the apparatus uses a refrigerant comprising, as a maincomponent, one of propane, isobutane and ethane, or a mixture of aplurality of these components, and uses refrigerating machine oil havingless mutual solubility with the refrigerant, and a dryer is provided inthe refrigeration cycle for absorbing water.

Since propane, isobutane and the like are refrigerants whose polaritiesare almost nonpolar, refrigerating machine oil having great polarity ispreferable as refrigerating machine oil having less mutual solubility,but refrigerating machine oil having great polarity is liable to absorbwater in the atmosphere, and if refrigerating machine oil which absorbswater is used as it is, the refrigerating machine oil is decomposed bystrong sliding movement of the mechanical portion of the compressor, andloss of the sliding movement is increased and sufficient reliability cannot be obtained. Therefore, in order to maintain the concentration ofwater in the refrigeration cycle at a low level, the dryer is disposedin the refrigeration cycle to absorb, fix and hold the water. With thisfeature, it is possible to obtain the sufficient reliability even in anapparatus having a refrigeration cycle using refrigerating machine oilhaving great polarity.

According to a second aspect of the invention, there is provided anapparatus having a refrigeration cycle, where the refrigeration cycle isformed by annularly connecting a compressor, a condenser, an expansiondevice and an evaporator with one another, the apparatus uses arefrigerant comprising, as main component, one of propane, isobutane andethane, or a mixture of a plurality of these components, and usesrefrigerating machine oil having less mutual solubility with therefrigerant, and an additive which reacts with water is included in therefrigerating machine oil.

By using an additive which reacts with water in the refrigeratingmachine oil, it is possible to easily maintain the concentration ofwater in the refrigeration cycle at low level without disposing anelement such as the dryer.

According to a third aspect, in the first or second aspect, therefrigerating machine oil is carbonate compound. A base oil of such arefrigerating machine oil is liquid material having linear or annularcarbon ester bond in molecular. The carbon ester bond has greatpolarizability, and the polarity of the compound having this carbonester bond in its molecular is big, it is possible to suppress themutual solubility with propane, isobutane or ethane of nonpolarity to asmall level, and it is possible to reduce the refrigerant in theapparatus having the refrigeration cycle.

According to a fourth aspect, in the third aspect, the number of carbonforming carbonic acid ester bond occupies at least 10 atomic % of allthe number of carbon forming the carbonate compound. By using thecarbonate compound having such a structure, greater polarity can beobtained, it is possible to further suppress the mutual solubility withpropane, isobutane or ethane of nonpolarity to a small level, and it ispossible to further reduce the refrigerant in the refrigeration cycle ofthe apparatus. Further, if a bond portion including hetero atom such asether bond, ester bond, amide bond or urea bond is included in a portionof the carbonate compound other than the carbon ester bond portion, thepolarity is further increased, and the mutual solubility can be furtherreduced.

According to a fifth aspect, in the third aspect, the purity of thecarbonate compound of the refrigerating machine oil is 99% or higher.With this feature, it is possible to suppress the sediment in theexpansion device generated from the refrigerant by controlling the totalamount of function group which has not yet reacted, and the sufficientlong term reliability can be obtained.

According to a sixth aspect, in the first or second aspect, mutualsolubility between the refrigerating machine oil and the refrigerant is5 wt % or less at 25° C. It is preferable that the mutual solubility is5 wt % or less in order to reduce the amount of refrigerant to becharged. It is difficult to completely suppress the refrigeratingmachine oil from being discharged from the compressor, and in order toagain collect, to the compressor, the refrigerating machine oil which isonce discharged from the compressor, it is possible to make it easytransfer the refrigerating machine oil by circulating refrigerant bygiving the mutual solubility to the refrigerating machine oil in somedegree, and the sufficient long term reliability can be obtained.

According to a seventh aspect, in the third aspect, the refrigeratingassembling oil includes 2 wt % or less of mineral oil or hardalkylbenzene with respect to the carbonate compound. When the mechanicalportion of the compressor is assembled, a certain amount of assemblingoil is required. It is possible to suppress the amount of water mixedfrom the atmosphere to a small level by using mineral oil or hardalkylbenzene as the assembling oil at the time of assembling, but sincethe assembling oil and the refrigerant are mutually dissolved in certaindegree, the amount of usage is limited to 2 wt % or less. If the amountof usage of the mineral oil or hard alkylbenzene is within this range,even if the assembling oil is used together with the refrigeratingmachine oil having less mutual solubility with the refrigerant, the longterm reliability can be ensured.

According to an eighth aspect, in the first or second aspect, kinematicviscosity of the refrigerating machine oil at 40° C. is in a range of 5to 20 cSt. With this feature, even if the refrigerating machine oilhaving less mutual solubility with the refrigerant is used, thelubricating performance and the sealing performance in the slidingportion of the compressor are not deteriorated, and the long termreliability can be ensured.

According to a ninth aspect, in the first or second aspect, kinematicviscosity of the refrigerating machine oil at 100° C. is in a range of 2to 5 cSt. With this feature, even if the refrigerating machine oilhaving less mutual solubility with the refrigerant is used, thelubricating performance and the sealing performance in the slidingportion of the compressor are not deteriorated, and the long termreliability can be ensured.

According to a tenth aspect, in the first or second aspect, dielectricconstant of the refrigerating machine oil is 30 or higher. With thisfeature, it is possible to suppress the mutual solubility between therefrigerant and the refrigerating machine oil, and the long termreliability can be ensured.

According to an eleventh aspect, in the first or second aspect, volumeresistivity of the refrigerating machine oil is 10¹¹ Ωcm or higher. Withthis feature, it is possible to suppress the leakage of electric currentdue to the refrigerating machine oil, and the long term reliability canbe ensured.

According to a twelfth aspect, in the first or second aspect, the amountof water in the refrigeration cycle is 50 ppm or less. That is, theamount of water existing in the refrigeration cycle is held by thedryer, or is reacted with the additive such that the amount of water iskept 50 ppm or less. With this feature, it is possible to limit thewater in the refrigeration cycle to the low concentration, to preventthe deterioration of refrigerating machine oil due to the decomposition,and to further ensure the long term reliability of the apparatus havingthe refrigeration cycle.

According to a thirteenth aspect, in the first or second aspect, theamount of oxygen in the refrigeration cycle is 800 ppm or less. Withthis feature, it is possible to ensure the safety of the flammablerefrigerant, to prevent the deterioration of the refrigerating machineoil due to oxidation, and to further ensure the long term reliability ofthe apparatus having the refrigeration cycle.

According to a fourteenth aspect, in the first aspect, the dryer isprovided in a liquid side pipe from the condenser to the evaporator.With this feature, it is possible to remove water more positivelywithout deteriorating the capacity of the refrigeration cycle due to theincrease of pressure loss, and to further ensure the long termreliability of the apparatus having the refrigeration cycle.

According to a fifteenth aspect, in the first aspect, the dryer isprovided in an oil reservoir in the compressor. With this feature, it ispossible to more positively remove water in the refrigerating machineoil which is liable to receive the influence of water, and to furtherensure the long term reliability of the apparatus having therefrigeration cycle.

According to a sixteenth aspect, in the first aspect, the dryer mainlycomprises K-exchange A-type zeolite. With this feature, propane,isobutane or ethane which is the refrigerant should not physically enterthe zeolite structure, and only water molecule is adsorbed and fixed andtherefore, it is possible to ensure the high long term reliability ofthe apparatus having the refrigeration cycle.

According to a seventeenth aspect, in the first aspect, the dryer mainlycomprises zeolite which is subjected to water repellent treatment. Withthis feature, it is possible to lower the reaction to high hydrophilicrefrigerating machine oil. Even if the surface of zeolite hasrepellency, there is no problem in water absorbing capacity in arefrigeration cycle whose pressure is high in some degree.

According to an eighteenth aspect, in the seventeenth aspect, the waterrepellent treatment of the zeolite is silane coupling. With thisfeature, silica surfaces of zeolite and clay used as bonding materialuniformly and strongly assume the repellency, and it is possible tofurther ensure the long term reliability of the apparatus having therefrigeration cycle.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view of a refrigeration cycle according to an embodiment ofthe present invention; and

FIG. 2 is a sectional view of a compressor according to the embodimentof the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

First, a structure of a refrigeration cycle and a compressor used in anembodiment of the present invention will be explained using thedrawings.

FIG. 1 shows the refrigeration cycle in an air conditioner, and FIG. 2shows a sectional view of the compressor used in the air conditioner.

As shown in FIG. 1, the compressor 1, a 4-way valve 2, an indoor heatexchanger 3, an expansion device 4 and an outdoor heat exchanger 5 areannularly connected with one another through pipes, thereby forming arefrigeration cycle. The indoor heat exchanger 3 functions as acondenser at the time of heating operation, and functions as anevaporator at the time of cooling operation. The outdoor heat exchanger5 functions as an evaporator at the time of heating operation, andfunctions as a condenser at the time of cooling operation.

As shown in FIG. 1, a dryer 6 for absorbing water is provided in aliquid side pipe between the indoor heat exchanger 3 and the outdoorheat exchanger 5.

As refrigerant used in the refrigeration cycle, propane or isobutane isused. As refrigerating machine oil in the compressor 1, refrigeratingmachine oil having less mutual solubility with the refrigerant is used.As such refrigerating machine oil, refrigerating machine oil comprisingcarbonate compound is effective, and carbonate compound in which thenumber of carbon forming carbonic acid ester bond occupies at least 10atomic % of all the number of carbon forming carbonate compound is moreeffective. It is preferable that mutual solubility between therefrigerant and the refrigerating machine oil is 5 wt % or less at 25°C. The dryer 6 includes K-exchange A-type zeolite as main material whichis calcined using clay of 25 wt % as bonding material. At that time, itis preferable that the zeolite is subjected to water repellent treatmentby silane coupling.

In such a refrigeration cycle, at the time of heating operation, theheat of the refrigerant which is compressed by the compressor 1 isreleased in the indoor heat exchanger 3, and the refrigerant isdecompressed by the expansion device 4, and absorbs heat in the outdoorheat exchanger 5, and is sucked into the compressor 1.

At the time of cooling operation, the refrigerant compressed by thecompressor 1 flows through the outdoor heat exchanger 5, the expansiondevice 4 and the indoor heat exchanger 3 in this order, and is suckedinto the compressor 1.

Water included in the refrigeration cycle circulates through therefrigeration cycle together with the refrigerant, and is absorbed bythe dryer 6 when the water passes through the dryer 6. By providing thedryer 6 in the liquid side pipe as shown in FIG. 1, the reducing amountby the expansion device 4 can be a value in which a pressure lossgenerated in the dryer 6 is taken into account, and the capacity of therefrigeration cycle can be kept appropriately.

FIG. 2 is a sectional view of the compressor 1 used in the presentembodiment.

The compressor 1 shown in FIG. 2 is a horizontal high pressure typescroll compressor in which a compressor mechanism 40, a motor mechanism50 and a pump 65 are laterally provided in a cylindrical shell 30. Thecompressor mechanism 40 comprises two scroll laps 47, 48, an oldham ring49 and the like. A refrigerant communication hole 91 is formed in thecompressor mechanism 40 for bringing a space A at the side of adischarge port 46 of the compressor mechanism 40 and a space B at theside of the motor mechanism 50 thereof into communication with eachother.

The motor mechanism 50 comprises a stator 51, a rotor 52 and the like. Agap 92 through which refrigerant gas passes through is formed betweenthe stator 51 of the motor mechanism 50 and the shell 30. The rotor 52and the scroll lap 47 are connected to each other through a crankshaft53.

An oil reservoir 60 is provided in a lower portion of the shell 30 at aportion closer to the motor mechanism 50 than the compressor mechanism40. The oil reservoir 60 is provided such that a dryer 100 is soaked inrefrigerating machine oil. The dryer 100 includes K-exchange A-typezeolite as main material which is calcined using clay of 25 wt % asbonding material. The dryer 100 may be disposed at any place if thedryer 100 can be soaked in the refrigerating machine oil sufficiently.In this regard, if the dryer 100 is disposed in the vicinity of anintake port of the pump 65 as shown in FIG. 2, refrigerating machine oilafter water is removed can effectively be supplied. However, since thedryer 100 is always in contact with the refrigerating machine oil undera high pressure condition, it is necessary to pay attention todecomposition of the refrigerating machine oil due to zeolite in view oflong term reliability.

An oil partition 66 is provided between the motor mechanism 50 and thepump 65. A lubrication groove is formed in the crankshaft 53 and theOldham ring 49 for supplying the refrigerating machine oil pumped upfrom the oil reservoir 60 by the pump 65 to the scroll laps 47 and 48. Arefrigerant discharging pipe 31 is provided closer to the pump 65 thanthe oil partition 66.

The flow of refrigerant gas and refrigerating machine oil of thecompressor will be explained below.

First, the refrigerant introduced into spaces in the scroll laps 47 and48 from an accumulator through an intake port 45 is compressed withturning movement of the movable scroll lap 47, and the compressed highpressure refrigerant gas is discharged from the discharge port 46 intothe space A. The refrigerant discharged into the space A is introducedthrough the refrigeration communication hole 91 into the space B betweenthe compressor mechanism 40 and the motor mechanism 50. The refrigerantpasses through a gap 92 between the stator 51 and the shell 30, andthrough the oil partition 66 and reaches an oil separating chamber 70,and is discharged from the refrigerant discharging pipe 31 out of theshell 30.

Water included in the refrigerating machine oil accumulated in the oilreservoir 60 is removed by the dryer 100 and then, the refrigeratingmachine oil is pumped up by the pump 65, and is supplied to slidingsurfaces of the scroll laps 47, 48 and the Oldham ring 49 through thelubrication groove formed in the crankshaft 53, the Oldham ring 49 andthe like. The refrigerating machine oil supplied into the compressorchamber is discharged into the space A from the discharge port 46together with the refrigerant, and is moved in the same manner as therefrigerant gas. However, the refrigerating machine oil discharged outtogether with the refrigerant is separated from the refrigerant when therefrigerating machine oil passes through the motor mechanism 50. Therefrigerating machine oil passing through the motor mechanism 50together with the refrigerant gas is separated from the refrigerant inthe oil separating chamber 70. The refrigerating machine oil separatedin this manner from the refrigerant is dropped to the oil reservoir 60.Most of refrigerating machine oil is introduced toward the pump 65 bythe stream of the refrigerant, but since the oil partition 66 isprovided, most refrigeranting machine oil is accumulated in the oilreservoir 60 in the oil separating chamber 70.

Although it is described that the dryer 6 is provided in therefrigeration cycle, and the dryer 100 is provided in the compressor 1,the dryer may be provided either one of them.

FIRST EMBODIMENT

In the refrigeration cycle of the apparatus shown in FIG. 1, 250 g ofpropane was used as refrigerant, and 250 g of carbonate compound of99.5% of purity represented by the following chemical formula and havingratio of 28% carbon forming carbonic acid ester bond was used asrefrigerating machine oil.

The dryer 6 was provided in the refrigeration cycle, and the dryer 100was not provided in the compressor 1.

The following series of reliability evaluation tests were conducted withrespect to the above-described apparatus having the refrigeration cycle,and no abnormality was found. An outdoor unit is disposed at a position5 m higher than an indoor unit.

Contents of test Condition Testing time 1 Cooling operation at highIndoor and outdoor units: 40° C. 1,000 hr temperature continuously 2Cooling operation at high Indoor and outdoor units: 40° C. 1,000 hrtemperature intermittently (ON for 26 min, Off for 4 min) 3 Heatingoperation at high Indoor and outdoor units: 24° C. 1,000 hr temperaturecontinuously 4 Heating operation at high Indoor and outdoor units: 24°C. 1,000 hr temperature intermittently (ON for 26 min, off for 4 min) 5Heating operation at low Indoor unit: 24° C., 1,000 hr temperaturecontinuously outdoor unit: −3° C. 6 Heating operation at low Indoorunit: 24° C., 1,000 hr temperature continuously (On for outdoor unit:−3° C. 1 hr, off for 5 hr) 7 Heating operation at low Indoor unit: 24°C., 1,000 hr temperature continuously outdoor unit: −3° C. (*Condition 1) * Condition 1: The outdoor unit is disposed at a position 5m higher than the indoor unit.

COMPARATIVE EXAMPLE 1

In the comparative example 1, 250 g of mineral oil was charged, arefrigeration cycle which was the same as that of the first embodimentwas formed, and a charging amount of propane required for obtaining thesame heating capacity was measured, and the result was 400 g.

Therefore, it was found that the charging amount of propane could bereduced by about 150 g, by using, as refrigerating machine oil, thecarbonate compound having less mutual solubility with propane as in thefirst embodiment.

SECOND EMBODIMENT

In the second embodiment, the dryer 6 shown in FIG. 1 was not used, and1 wt % of epoxy compound which reacted with water in some degree underhigh temperature and high pressure was added in the same refrigeratingmachine oil as that of the first embodiment, and the resultantrefrigerating machine oil was charged. In the present embodiment also,the dryer 100 was not provided in the compressor 1.

The same reliability evaluation tests as those of the first embodimentwere conducted with respect to the apparatus having the refrigerationcycle of the second embodiment and as a result, no abnormality wasfound.

Although the refrigerating machine oil in which 1 wt % of epoxy compound(molecular weight: 306) was added was used in the present embodiment,additive that can be used in the present invention is not be limited tothis. Other additive that reacts with water and becomes stable alcoholradical or the like may be used. However, epoxy compound having highreactivity also reacts with carbonate compound, water in therefrigeration cycle can not be absorbed, and sediment is produced in anexpansion device in which flowing speed is reduced, which may cause afactor to reduce the flow rate. Further, if the amount of additive addedto the refrigerating machine oil is not controlled in some degree,additives having inferior stability are polymerized with each other,which may cause a factor to produce sediment in the expansion device toreduce the flow rate. Therefore, the additive amount was 2 wt % or less,and more preferably, 1 wt % or less.

THIRD EMBODIMENT

In the third embodiment, the dryer 6 was not used, and the dryer 100 inthe compressor 1 was used. K-exchange A-type zeolite as main materialwhich was calcined using clay of 25 wt % as bonding material wasincorporated in the dryer 100.

Refrigerant and refrigerating machine oil were the same as those in thefirst embodiment.

As a result, it was possible to fix and hold water in the refrigerationcycle by zeolite faster than the first embodiment.

FOURTH EMBODIMENT

In the fourth embodiment, K-exchange A-type zeolite as main material wascalcined using clay of 25 wt % as bonding material, and the resultantmaterial was sufficiently subjected to coupling treatment usingtrimethylchlorosilane for water repellent, and was used as the dryer 6in the first embodiment.

The same series of reliability evaluation tests as those in the firstembodiment were conducted with respect to the present embodiment. As aresult, the amount of non-condensed gas generated due to decompositionof the refrigerating machine oil was smaller than the first embodiment.It is considered that this result was caused because the dryer whichmainly comprises zeolite was provided with repellency so that theabsorption and adhesion of the refrigerating machine oil could besuppressed, it was possible to prevent zeolite from acting as a reactionplace of decomposition of the refrigerating machine oil.

In the present embodiment, in order to make zeolite have repellency,silane coupling treatment was conducted, but repellent treatment thatcan be applied to the present invention is not limited to this.Alternatively, it is possible to treat with a Teflon-based compound.However, it is considered that the silane coupling is most preferable inview of congeniality with zeolite to be treated and retention strengthof the water repellent film.

The above embodiments have been explained using the horizontal highpressure type scroll compressor as the compressor, the compressorapplicable to the present invention is not limited to this, and othercompressors of rotary type, helical type, linear type and the like canalso be used. Since the mechanical structure of the scroll compressorused in the present embodiment is complicated, although about 4 g ofhard alkylbenzene (1.6 wt % of the refrigerant) was used as assemblingoil, but abnormality due to this was not detected as a result ofreliability evaluation tests. If the mechanism is assembled withoutusing this assembling oil, the members were damaged such as flaw in manycases, and the yield was largely reduced. Further, if the assembling oilwas not used in cold winter season, adhesion of water was caused due todropwise condensation more frequently as compared with a case in whichthe assembling oil was used. Therefore, it is considered that it ispreferable to effectively use the appropriate amount of assembling oilwhich hardly absorbs water in the atmosphere. In the case of a linearcompressor or a single rotary compressor having a simple mechanicalstructure, a necessary amount of assembling oil could be smaller thanthat of the scroll compressor, and the amount was about 1 to 2 g. It isconsidered that the apparatus can be produced with high productivity bycontrolling the amount of assembling oil to 2 wt % or less with respectto refrigerating machine oil in view of structures of variouscompressors.

Although carbonate compound (ratio of 28% carbon forming carbonic acidester bond) represented by the chemical formula (1) was used asrefrigerant in the above embodiments, it was found that it is preferablethat the ratio of the number of carbon forming the carbonic acid esterbond is 10 atomic % or higher with respect to the total number of carbonforming carbonate compound so as to suppress the solubility with thepropane, isobutane and ethane to a small value. However, if the ratioexceeds 30 atomic %, thermal stability as refrigerant is largelydeteriorated, and it is considered that the optimal range is 10 to 30atomic %.

In the above embodiments, carbonate compound of 99.5% of purity wasused, and its producing method will be described below.

Methanol solution of ethylene glycol, dimethyl carbonate and sodiummethoxide was charged in a predetermined container having a distillationcolumn, and it was heated under normal pressure at 110 to 150° C. for 8hours to distill ethanol to be generated, and the temperature wasincreased up to 200° C. under vacuum to distil residue diethylcarbonate. Tetrahydrofuran was charged into the obtained reactionmixture and diluted and then, the mixture was passed through a column inwhich ion-exchange resin amberyst 15 (trade name) to neutralize andremove residue catalyst and then, the tetrahydrofuran was distilled andremoved to obtain the carbonate compound (represented by the chemicalformula 1). Therefore, material having high reactivity did not remain,but it was necessary to control to restrict impurities which were notthe desired carbonate compound so as to obtain long term reliability asan apparatus having a refrigeration cycle. More specifically, althoughyield and kinds of impurities differed depending upon the desiredcarbonate compound, in the case of carbonate compound applicable to thepresent invention, it was necessary to control the purity to 99% ormore, and more preferably, 99.5% or more.

Although K-exchange A-type zeolite was used as a content of the dryer inthe embodiments, zeolite that can be used in the present invention isnot limited to this. Na-exchange type and Ca-exchange type zeolite couldbe used without any problem. In the case of Na-exchange type andCa-exchange type zeolite, propane refrigerant entered in the structureof zeolite, but since water absorption strength of zeolite was stronger,propane refrigerant gradually substituted for water, and water wasabsorbed and fixed. However, it is considered that it is most preferableto select K-exchange type zeolite so as to positively absorb and fixonly water (diameter of molecular: 0.28 nm) in the structure of zeolitein view of fine hole diameter of zeolite structure.

The present invention uses refrigerating machine oil having less mutualsolubility with refrigerant comprising, as main component, one ofpropane, isobutane and ethane, or a mixture of a plurality of thesecomponents. Therefore, viscosity of the refrigerant used in the presentinvention is very small as compared with refrigerant having high mutualsolubility with refrigerant. Further, in the case of the refrigeratingmachine oil having the high mutual solubility, the refrigerant wasmelted in the refrigerating machine oil to lower the viscosity at a lowtemperature, and the refrigerant was discharged from the refrigeratingmachine oil at a high temperature, and the refrigerating machine oilhaving the high mutual solubility was used as hydraulic fluid in a statewhere the viscosity thereof is close to that of the refrigeratingmachine oil itself by lowering the viscosity. However, in the case ofthe refrigerating machine oil having less mutual solubility, since themutual tendency between the viscosity and the temperature of therefrigerating machine oil itself directly affects the performance of thecompressor, it is preferable that the viscosity dependency with respectto the temperature is as low as possible. In view of the oil seal andefficiency of the compressor, it was preferable that kinematic viscosityat 100° C. was 2 to 5 cSt, and kinematic viscosity at 40 was 5 to 20cSt.

The present invention intends to use refrigerating machine oil havingless mutual solubility with refrigerant comprising, as main component,one of propane, isobutane and ethane, or a mixture of a plurality ofthese components, and as a result of hard research therefor, it wasfound that it was possible to lower the mutual solubility by increasingdielectric constant of refrigerating machine oil. More specifically, itis considered that if the dielectric constant is 30 or higher, arefrigerant having, as a main component, a one of propane, isobutane andethane, or a mixture of a plurality of these components can be included.

Since the present invention intends to use refrigerating machine oilhaving less mutual solubility with refrigerant comprising, as a maincomponent, one of propane, isobutane and ethane, or a mixture of aplurality of these components, it is not possible to expect volumeresistivity of 10¹³ Ωcm or greater unlike the conventional mineral oil.However, if measures for current leakage as an apparatus having arefrigeration cycle are taken into account, characteristic equal to orgreater than 10¹¹ Ωcm was required even if the refrigerating machine oilhas great polarity.

Since the present invention intends to use refrigerating machine oilhaving less mutual solubility with refrigerant comprising, as a maincomponent, one of propane, isobutane and ethane, or a mixture of aplurality of these components, refrigerating machine oil having greathygroscopicity is used. At that time, if water remains free in therefrigerating machine oil, refrigerating machine oil is easilydecomposed under a high temperature condition of the sliding portion ofthe compressor, and this acts as a trigger to develop excessivedecomposition of the refrigerating machine oil. Furthermore, the flowrate of the decomposed material was lowered around the expansion deviceof the refrigeration cycle, the decomposed material became sediment ontopipe wall, and the pipe might be choked. Therefore, it was necessary tocontrol the water in the refrigeration cycle at 50 ppm or less,preferably, 30 ppm or less so as to obtain the long term reliability asan apparatus having the refrigeration cycle.

Since the present invention intends to use refrigerating machine oilhaving less mutual solubility with refrigerant comprising, as maincomponent, one of propane, isobutane and ethane, or a mixture of aplurality of these components, refrigerating machine oil having greathygroscopicity is used. Such a refrigerating machine oil was inferioralso in thermal resistance to conventional mineral oil and the like, ifa great amount of residue oxygen exists in the refrigeration cycle, theresidue oxygen was easily taken into the refrigerating machine oil undera high temperature condition of the sliding portion of the compressor,or reversely, the oxygen was combined with refrigerating machine oildecomposed material into compound. Therefore, it was necessary tocontrol the oxygen in the refrigeration cycle at 800 ppm or less,preferably, at 500 ppm or less so as to obtain the long term reliabilityas an apparatus having the refrigeration cycle.

As apparent from the above-described embodiment, according to thepresent invention, it is possible to prevent the deterioration and thedecomposition of refrigerating machine oil, to reduce the chargingamount of refrigerant by using refrigerating machine oil having lessmutual solubility with the refrigerant, and to provide a high safetyapparatus having a refrigeration cycle.

What is claimed is:
 1. An apparatus having a refrigeration cycle, wheresaid refrigeration cycle is formed by annularly connecting a compressor,a condenser, an expansion device and an evaporator with one another,said apparatus uses a refrigerant comprising, as a main component, oneof propane, isobutane and ethane, or a mixture of a plurality of thesecomponents, and uses refrigerating machine oil, wherein a mutualsolubility between said refrigerating machine oil and said refrigerantis 5 wt % or less at 25° C., and an additive which reacts with water isincluded in said refrigerating machine oil.
 2. An apparatus having arefrigeration cycle according to claim 1, wherein said refrigeratingmachine oil is carbonate compound.
 3. An apparatus having arefrigeration cycle according to claim 2, wherein in said refrigeratingmachine oil, the number of carbon atoms forming a carbonic acid esterbond is at least 10 atomic % of all the number of carbon atoms formingsaid carbonate compound.
 4. An apparatus having a refrigeration cycleaccording to claim 2, wherein the purity of said carbonate compound ofsaid refrigerating machine oil is 99% or higher.
 5. An apparatus havinga refrigeration cycle according to claim 2, wherein said refrigeratingmachine oil includes 2 wt % or less of mineral oil or hard alkylbenzenewith respect to said carbonate compound.
 6. An apparatus having arefrigeration cycle according to claim 1, wherein kinematic viscosity ofsaid refrigerating machine oil at 40° C. is in a range of 5 to 20 cSt.7. An apparatus having a refrigeration cycle according to claim 1,wherein kinematic viscosity of said refrigerating machine oil at 100° C.is in a range of 2 to 5 cSt.
 8. An apparatus having a refrigerationcycle according to claim 1, wherein dielectric constant of saidrefrigerating machine oil is 30 or higher.
 9. An apparatus having arefrigeration cycle according to claim 1, wherein volume resistivity ofsaid refrigerating machine oil is 10¹¹ Ωcm or higher.
 10. An apparatushaving a refrigeration cycle according to claim 1, wherein the amount ofwater in said refrigeration cycle is 50 ppm or less.
 11. An apparatushaving a refrigeration cycle according to claim 1, wherein the amount ofoxygen in said refrigeration cycle is 800 ppm or less.